Bubble detector having detection depends on position of impingement of the light beam

ABSTRACT

A bubble detector includes a conduit (1) through which a first fluid having a first refractive index is intended to flow, a light source (3) which directs a light beam (4; 41, 42) through a transparent conduit wall-part (12), through the conduit cavity and out through a second transparent conduit wall-part, and a detector means (5; 51, 52, 53) adapted to receive the light beam (4, 41) after the beam has passed through the conduit and the first fluid therein. The two opposing transparent wall-parts (12, 11) of the conduit (1) are trans-illuminated by the light beam and are essentially planar and parallel. The light source (3) is adapted to direct the beam (4) at an oblique angle (α) to the proximal transparent wall-part (12) of the conduit (1), so that the light source will be broken into different paths (41, 42) depending on whether the beam passes the first fluid or a second conduit-carried fluid having a different refractive index, such as a bubble. The detector means (5; 53; 51, 52) is adapted to be impinged upon by the beam (4, 42) exiting from the conduit (1) irrespective of the refractive index of the fluids, and the detector means (5; 53; 51, 52) is adapted to deliver an output signal that is dependent on the position at which the beam (41, 42) impinges on the detector means, so as to enable the occurrence of bubbles in the first fluid to be identified.

The invention relates to a bubble detector of the kind defined in thepreamble of the following Claim 1.

BACKGROUND OF THE INVENTION

Earlier known technology is described in FR-A1-2 660 755, whichdiscloses a bubble detector that includes a conduit through which afirst fluid having a first refractive index passes, a light source whichdirects a light beam through a first transparent wall part of theconduit, through the conduit cavity, and out through a secondtransparent wall part of said conduit, and a detector means whichreceives the light beam after it has passed through the conduit and thefirst fluid present therein. It is also disclosed in FR-A1-2 660 755that the light beam shall be directed in a plane normal to the axis ofthe circular-cylindrical conduit and be directed non-diametricallythrough said conduit. With this construction, it is necessary toaccurately adjust the position and direction of the light source withrespect to refractive index (the first fluid/liquid concerned), and theposition of the detector must be adjusted to receive the light beam.This known arrangement presumes that the refractive index of the fluidis constant and will record error functions already at relatively smallvariations in the refractive index of the fluid. The reliability of theknown arrangement is also relatively poor, because the presence ofbubbles in the fluid is detected by non-detection of a light beam by thedetector. When the light beam passes a bubble, the beam is split andspreads so that no clear light beam will leave the conduit.

Among other drawbacks with the known arrangement is that it gives noclear indication of malfunctioning of the main components.

The object of the present invention is to reduce or eliminate at leastone of these drawbacks.

This object is achieved with a bubble detector according to theaccompanying Claim 1.

SUMMARY OF THE INVENTION

The dependent Claims define further embodiments of the detector.

The invention is based on the fundamental concept that the twotransparent conduit wall-parts that are trans-illuminated by the lightbeam shall be essentially flat and parallel and that the light beam isdirected through the conduit at an oblique angle, e.g. 45 degrees, tothe nearest plane of the trans-illuminated wall-part, so that the lightbeam will be broken into different paths depending on whether the beamin the conduit passes through the first fluid or through bubbles of asecond fluid having a different refractive index. The detector means istherewith adapted to be impinged upon by the light beam exiting from theconduit independently of refractive index for the fluid or fluid mixturepresent between the two conduit wall-parts. The detector means isadapted to deliver an output signal that depends on the position atwhich the light beam meets the detector means, so as to enable thepresence of bubbles of said second fluid in said first fluid to beidentified by corresponding variations in the detector output signal.

In a preferred embodiment of the invention, the detector means includesa difference photodiode which delivers a signal that depends on theposition at which the light beam meets the diode surface. A detectormeans of this nature can be readily calibrated; the first fluid, e.g. aliquid, can be passed through the conduit while ensuring that the firstfluid is free from bubbles or the like. The signal that defines abubble-free state of the first fluid is noted at the same time. A givendeviation from this output signal will indicate a change in therefractive index of the medium in the conduit, that the detector meansis malfunctioning, or that the alignment of the light source in relationto the conduit and/or the detector has been changed. Because the changein output signal is the result of a displacement in the distance of theposition of contact of the light beam from the calibrating position,there will always be obtained an output signal from the detector meansprovided that the light source is operative and said arrangement has notbroken down.

In a simplified variant of the invention, the detector means may includemutually separated, simple photodetectors instead of a differencephotoelectrode. In this case, one photodetector is placed in a positionin which it will be met by the light beam when passing through abubble-free first fluid, and the other detector is placed in a positionin which it will only be met by the light beam when said beam passesthrough a fluid in the conduit that has a different refractive index tosaid first fluid.

When the conduit is circular-cylindrical, the conditions whereby theconduit wall-parts trans-illuminated by the light beam are essentiallyplanar and parallel can still be established, provided that it isensured that the beam is narrow and cuts the conduit axis in its variousrefractive-index dependent paths. Thus, the path of the light beam willpreferably lie in a plane that includes the conduit axis.

However, it will be obvious that the trans-illuminated wall-parts arepreferably plane-parallel wall parts, so that the position at which thelight beam meets said parts is not critical.

Because of the inventive concept, positive information is obtained fromthe detector means in the form of an output signal both when the conduittransports bubble-free fluid and when bubbles are present in the fluidflow, or when solely gas is present in the conduit.

Furthermore, information is obtained with regard to malfunctioning ofthe light source or malfunctioning of the detector means, bydisappearance of the output signal.

Thus, the inventive detector means can be used to control the flow offluid through the conduit and/or to trigger an alarm when bubblesappear, or when the detector output signal disappears completely.

The invention or forms thereof is defined in the following Claims.

An exemplifying embodiment of inventive arrangements will now bedescribed with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an axial sectional view of a schematically illustratedembodiment of the invention.

FIG. 2 is a sectional view taken on the line II--II in FIG. 1.

FIGS. 3 and 4 illustrates alternative embodiments of the inventivedetector in the detector means.

FIG. 5 is a schematic illustration corresponding to FIG. 2 and shows theinvention as applied to a conduit of rectangular cross-section.

DETAILED DESCRIPTION OF THE DRAWINGS

It will be apparent from FIGS. 1 and 2 that the inventive bubbledetector includes a light permeable conduit 1, whose longitudinal axisis referenced 2. Liquid flows through the conduit 1 in the direction ofits axis 2. The bubble detector functions to detect a gas bubble, suchas an air bubble, in the liquid flow, said gas and liquid being assumedto have mutually different refractive indexes.

A light source 3 directs a light beam 4 through the conduit 1 at anoblique angle α to the axis 2. By "oblique" is meant an angle α that isgreater than 0 and smaller than 90°, preferably an angle in the range of30-60°, for instance about 45°. The conduit 1 shall be permeable tolight at the two wall-parts 11, 12 through which the beam 4 passes.

The light beam 4 will take different paths through the conduit 1,depending on the refractive index of the medium located in the path ofthe light beam within the conduit 1. Thus, the light beam 4 will takethe path 41 when the fluid in the conduit has essentially the samerefractive index as the material from which the conduit 1 is made, as inthe case when a liquid, such as water, flows through the conduit 1. Thelight beam 4 will take the path 42 in FIG. 1 when the fluid in theconduit has a refractive index that is significantly lower than that ofa liquid, for instance when the fluid is air.

The conduit 1 has a cross-sectional size that corresponds to a bubblesize that is considered to be dangerous or harmful, such that a bubblewill be unable to pass through the conduit 1 by the side of the lightbeam 4; 41, 42.

It will be seen from FIG. 1 that the two beam paths 41, 42 areessentially parallel but separated when exiting from the conduit 1. Thedetector means 5 that receives the beams 41, 42 includes a detector 53,preferably a conventional difference photodiode, which delivers a signalwhose magnitude depends on the position of impingement of the beam alongthe surface of the diode 53. Thus, the different output signals obtainedfrom the positions of impingement of the beams 41, 42 can be easilydistinguished from one another, and a further advantage afforded by adifference photodiode is that its position need not be adjusted inaccordance with different refractive indexes of the liquid.

The bubble detector can thus be easily calibrated, by noting the outputsignal obtained in respect of a bubble-free liquid that has a knownrefractive index. When the characteristics of the detector are known,the refractive index of an unknown (bubble-free) fluid can be determinedby the output signal obtained in respect thereof, this output signalthus being dependent on the position of impingement of the beam.

In the embodiment illustrated in FIGS. 1 and 2, the conduit 1 has acircular-cylindrical configuration. It is important in this case thatthe beams 4, 41, 42 intersect the conduit axis 2 so that thetrans-illuminated wall-parts 11, 12 are planar and parallel in practice.However, when the conduit 1 is configured so as to have actually twoflat plane-parallel wall-parts 11, 12 of uniform thickness, asillustrated in FIG. 5, the throughflow direction/axis 2 of the conduit 1and the light beams 4, 41, 42 need not, of course, lie in a commonplane, as will be evident from a study of FIG. 5.

FIG. 3 illustrates a simplified embodiment of the invention in which thedetector means 5 includes two separated detectors 51, 52 that arepositioned to receive the beam 41 and the beam 42 respectively. Asbefore mentioned, it is difficult to adjust such a simplified detectormeans for liquids and bubbles of mutually different indexes. A prism 60which functions to deflect the beams 41, 42 to the two detectors 51, 52may be provided with the intention of obtaining a sharper definitionbetween the two detectors 51, 52.

When the presence of a bubble or gas in the conduit is consideredhazardous, it is obvious that the disappearance of one output signalfrom the detector corresponding to the signal 41 will constitute analarm situation, and that an output signal corresponding to impingementof the beam 42 on the detector means will also constitute an alarmsituation. The inventive arrangement thus obtains a significantredundancy. Because the detector means (or always at least one of thedetectors 51, 52) will always deliver an output signal in response to anoperable light source 3, there is immediately obtained an indicationwhen the light source 3 malfunctions. An alarm indication is also givenwhen the detector means 53 or one of the detectors 51, 52 has no outputsignal, this alarm indication being given immediately when the lightsource or the detector means malfunctions in some way or another. Theillustrated arrangement includes a monitoring unit 20 which functions tocontrol the transport of liquid through the conduit 1, for instance byclosing a valve in the conduit in the event of an alarm indication. Theunit may conveniently include an alarm means that is triggered inresponse to an alarm indication.

The invention finds general use in conjunction with the transportationof fluid through a conduit where it is important that fluidtransportation can be stopped or that at least an alarm of some kind isgenerated when the refractive index of the fluid changes, such as whenthe fluid is a liquid that may not contain bubbles or be replaced withgas. The invention is therefore particularly useful in conjunction withthe infusion of fluids to the blood circulation of the human body.

The conduit 1 will preferably have an inner diameter that is at maximumessentially equal to a bubble size that is considered hazardous, so thatthe beam 4 will always take the path 42 when a hazardous bubble passesthrough the conduit.

What is claimed is:
 1. A bubble detector comprising a conduit (1)through which a first fluid having a first refractive index is intendedto flow, a light source (3) that directs a light beam (4; 41, 42)through a transparent conduit wall-part (12) and through the conduitcavity and out through a second transparent conduit wall-part, and adetector means (5; 51, 52, 53) which is adapted to receive the lightbeam (4, 41) when the beam has passed through the conduit and the firstfluid therein, characterized in that the two mutually oppositetransparent wall-parts (12, 11) of the conduit (1) that aretrans-illuminated by the light beam are essentially planar and parallel;in that the light source (3) is adapted to direct the light beam (4) atan oblique angle (α) to the proximal transparent conduit wall-part (12)so that the light beam is broken into different paths (41, 42) dependingon whether the beam passes the first fluid or a second conduit-conductedfluid having another refractive index, such as a bubble; in that thedetector means (5; 53; 51, 52) is adapted to be impinged upon by thelight beam (4, 42) exiting from the conduit (1) irrespective of therefractive indexes of the fluids; and in that the detector means (5; 53;51, 52) is adapted to deliver an output signal that depends on theposition of impingement of the light beam (41, 42) on the detectormeans, so as to enable the occurrence of bubbles in the first fluid tobe identified.
 2. A detector according to claim 1, characterized in thatthe conduit is generally cylindrical, preferably circular-cylindrical;and in that the light beams (4, 41, 42) exiting from the light source(3) and the conduit axis (2) lie in a common plane.
 3. A detectoraccording to claim 1, characterized in that the detector means isadapted to trigger an alarm and/or to stop the transportation of thefirst fluid through the conduit (1) when the position of impingement ofthe light beam on the detector means deviates from the position ofimpingement that corresponds to the light beam passing through abubble-free first fluid in the conduit.
 4. A detector according to claim1, characterized in that the detector means (5; 53; 51, 52) is coupledto monitoring logic that functions to trigger an alarm and/or stoptransportation of fluid through the conduit (1) when the output signaldisappears.
 5. A detector according to claim 1, characterized in thatthe detector means is a difference photodiode (53) which delivers anoutput signal that is dependent on the position of impingement of thelight beam (41, 42) on the diode's surface.